JPH04304290A - Phosphor and its manufacture - Google Patents

Abstract

PURPOSE:To provide a new phosphor improved in thermal quenching, chemical stability and service life and a method of manufacture thereof by utilizing the excellent thermal conductivity, light transmittance, and chemical stability of diamond. CONSTITUTION:A phosphor which has a thin diamond layer deposited on the surface of phosphor particles by the microwave plasma method. A method of manufacture of the phosphor comprises generating microwave plasma in a part of the interior of a rotating reactor 4 isolated from the air and kept under a reduced pressure inside, and continuously supplying phosphor particles 12 by the rotation and gradient of the reactor 4 to the region 36 where microwave plasma is generated while blowing a hydrogenmethane gas mixture 10 into the region 36, thus forming a thin diamond layer on the surfaces of the phosphor particles 12.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention forms a diamond thin film layer on the surface of phosphor particles by microwave plasma method, and utilizes diamond's excellent thermal conductivity, light transmission characteristics, and chemical stability. This invention relates to a new phosphor with improved temperature quenching, chemical stability and lifetime, and a method for producing the same.

0002

2. Description of the Related Art In recent years, a microwave plasma method has been attracting attention as a method for stably synthesizing diamond film on the surface of a substrate. In this microwave plasma method, for example, as shown in Japanese Patent Application Laid-Open No. 58-110494,
Hydrogen-methane mixed gas transmitted through microwave plasma is introduced onto the substrate surface heated to 300° C. to 1300° C., and diamond can be deposited on the substrate surface by thermal decomposition of hydrocarbons.

0003

[Problem to be Solved by the Invention] However, in the above-mentioned microwave plasma method, diamond is deposited on the surface of a substrate such as molybdenum or silicon wafer, and it is difficult to apply it directly to powder particles different from the substrate. For example, methods have been proposed in which a fluidized bed is formed and diamond is precipitated on the powder surface, as in JP-A-59-137311 and JP-A-63-270394. These methods are essentially batch processes, and are not suitable for continuous processing in the case of industrial mass production because the equipment becomes complicated. Furthermore, it is extremely difficult to fluidize fine particles of several micrometers such as phosphor particles, and it is desired to develop a new method for depositing diamond on the surface of powder particles of several micrometers.

On the other hand, with regard to phosphors, although in recent years there has been a desire for higher brightness of the light-emitting surface due to the higher definition and larger size of television and display screens, the high load of the excited electron beam has increased. The high current causes problems such as the brightness saturation characteristics, temperature characteristics, and life span of the phosphor particles in the phosphor screen, and the improvement in the brightness of the phosphor screen is stagnant. In particular, in projection tubes in which the current and voltage for exciting the phosphors are high, it is strongly desired to improve the brightness saturation characteristics, temperature characteristics, and lifespan of the phosphors.

[0005] Therefore, the object of the present invention is to provide a new phosphor that has improved temperature quenching, chemical stability, and lifetime by utilizing the excellent thermal conductivity, light transmission characteristics, and chemical stability of diamond. An object of the present invention is to provide a method for manufacturing the same.

[0006]

[Means for Solving the Problems] In order to form a high-quality diamond thin film layer on the surface of phosphor particles by a microwave plasma method, the present inventors have first developed a method that is suitable for phosphor particles of several μm and that is suitable for industrial use. We have developed a new device capable of continuous operation of powder particles, which is useful in terms of productivity, and have succeeded in forming a diamond thin film layer of a desired thickness on the surface of phosphor particles.

That is, the phosphor of the present invention is characterized in that it has a diamond thin film layer deposited by a microwave plasma method on the surface of the phosphor particles.

[0008] Furthermore, in the method for producing a phosphor of the present invention, microwave plasma is generated in a part of a rotating reaction vessel that is airtightly isolated from the outside air and maintained at a reduced pressure inside, and the microwave plasma is generated in the microwave plasma generation region. At the same time as hydrogen-methane mixed gas is introduced, phosphor particles are continuously supplied to the microwave plasma generation region by rotating and tilting the rotating reaction vessel.
This method is characterized in that a diamond thin film layer is formed on the surface of the phosphor particles.

[0009]

[Operation] By forming a uniform diamond thin film layer on the surface of the phosphor particles using the microwave plasma method,
Diamond's excellent thermal conductivity, light transmission properties and chemical stability can be utilized to improve temperature quenching, chemical stability and lifetime. This is itemized below. (2) In particular, by coating a phosphor used when the temperature of the phosphor film is large, such as a phosphor for a projection tube, with a diamond thin film layer, heat dissipation is achieved, and brightness deterioration due to temperature quenching can be improved. ■ Uniform diamond thin film layer prevents ion burning and compositional changes on particle surfaces. ■No color center is formed due to diffusion of impurities from the outside. (2) It is possible to improve phosphors that conventionally deteriorate significantly due to hydrolysis, such as alkaline earth metal salt phosphors and lanthanum oxysulfide phosphors. (2) Since the surface of the phosphor is a diamond thin film layer of the same type, uniform coating characteristics can be achieved even if the phosphor matrix composition differs. ■Since the surface of the phosphor is a uniform diamond thin film layer, it is possible to improve adhesion to the glass surface to be coated.

[0010] Furthermore, according to the method for producing a phosphor of the present invention,
A diamond thin film layer of a desired thickness can be easily and industrially and continuously formed on the surface of phosphor particles, and a phosphor with improved temperature quenching, chemical stability, and lifetime can be obtained. can.

[0011]

[Example] Hereinafter, examples of the present invention will be described in detail with reference to the drawings.Prior to the description of the examples, a diamond coating device newly developed by the present inventors will be explained for carrying out the present invention. do.

FIG. 1 shows a schematic cross-sectional view of a diamond coating apparatus capable of coating a desired diamond thin film layer on the surface of powder particles. This apparatus has a tubular rotating reaction vessel 4 which is rotatably supported at both ends by a base via suitable roller means 2 and is capable of holding any inclination angle.

One end of the rotating reaction vessel 4 on the inclined upper side (left side in FIG. 1) is airtightly connected via a rotor joint 6 to a screw feeder 8 for supplying powder. One end of the screw feeder 8 is airtightly connected to a source gas source 10 containing at least methane-hydrogen mixed gas via a source gas supply port in order to deposit diamond. A powder supply device 12 is provided at the top of the device, and this powder supply device 12 is connected to a back pressure gas source 14 of hydrogen gas via a back pressure gas port.

On the other hand, a collector 18 for collecting powder is airtightly provided at one end of the lower inclined side of the rotating reaction vessel 4 (on the right side in FIG. 1) via a rotor joint 16. A powder collecting section 20 is provided at the lower part of the collector 18. A gas transport pipe 22 is connected to the upper part of the collector 18, and this gas transport pipe 22 is further connected to another transport pipe 26 via a bag filter 24. Depending on the particle size of the powder, that is, in the case of fine powder, the powder is collected at the lower part of the bag filter 24.

By the way, the rotary reactor 4 is installed so as to pass through a microwave cavity 28, and this microwave cavity 28 is connected to a microwave oscillator 32 through a waveguide 30. A plunger 34 for reflecting microwaves is disposed on the other side of the waveguide 30 that faces the microwave oscillator 32 with the rotating reactor 4 in between. During operation, microwaves from a microwave oscillator 32 pass through the rotating reaction vessel 4 and a microwave plasma reaction area 36 is generated in the center of the rotating reactor 4 by the action of the microwave cavity 28 and the plunger 34.
is formed.

Referring to FIG. 2, as is clear, powder particles are stably supplied into the rotary reactor 4, and diamond is coated on each particle during feeding to the microwave plasma reaction region 26. In order to precipitate the
8 is formed, and as the rotary reactor 4 rotates, the powder is stably supplied in a gradually dispersed state along the inclination direction of the rotary reactor 4.

Next, the operation of the diamond coating apparatus constructed as described above will be described.

First, the transport pipe 26, bag filter 24, transport pipe 22 and collector 18 are removed by a vacuum pump (not shown).
The pressure inside the rotating reaction vessel 4, the waveguide 30, and the screw feeder 8 is reduced to a predetermined pressure via the . At the same time, raw material gas is supplied from the raw material gas source 10 through the screw feeder into the rotating reaction vessel 4 and into the waveguide 30, and at the same time, by operating the microwave oscillator 32, the waveguide 30 and the plunger 34 generate microwave plasma. is opening 26
Hydrocarbons in an excited state, hydrogen in an excited state or an atomic state are generated from the raw material gas, and thereby a microwave plasma reaction region 36 is formed.

On the other hand, powder particles are supplied into the rotating reaction vessel 4 via the powder supply device 12 and the screw feeder 8, and the powder supplied into the rotating reaction vessel 4 is supplied to the raw material gas source 1.
The fluidity is increased by supplying the raw material gas from 0, and the raw material gas is gradually supplied to the microwave plasma reaction region 26 by the stirring blade 38. Note that the particles are heated to a predetermined temperature by the action of microwaves and plasma.

[0020] Then, the microwave plasma reaction region 36
The excited hydrogen and hydrocarbons are transported to generate a plurality of types of hydrocarbon radicals, which become elementary and coat the powder surface in the microwave plasma reaction region with a diamond thin film layer. Thereafter, the powder is gradually moved within the rotating reaction container 4 by the rotation of the rotating reaction container 4 again, and the powder is collected in the powder collecting section 20 . On the other hand, the remaining particulates and gas components are introduced into the bag filter 24 via the transport pipe 22, the remaining particulates are separated in the lower part of the bag filter 24, and the gas components are introduced into the bag filter 24 through the transport pipe 26 and a vacuum pump (not shown). It is then exhausted.

The conditions for diamond precipitation in the microwave plasma reaction region 26 will be described below, particularly when applied to phosphor particles of several μm to more than ten μm. Total amount of gas supply: 100sccm. Raw material gas source 10
Gas supply amount from 50sccm. Gas supply amount from back pressure gas source 14: 50 sccm.

The gas components of the source gas source 10 include methane-
Water vapor and hydrogen sulfide gas may be mixed as an additive gas to the hydrogen mixed gas in order to prevent the matrix composition of the phosphor from changing due to melting with the plasma and deposit high quality diamonds, while back pressure gas The gas from the source 14 is hydrogen gas, and taking this hydrogen gas into account, the gas mixture ratio is as follows. CH4 concentration (CH4/H2 ratio) O. 1-10%. Preferably 0.1 to 1.0%. H2O concentration (H2O/CH4 ratio) O~500%. Preferably 30-100%. H2S concentration (H2S/CH4 ratio) O~500%. Preferably 50-150%.

The pressure, processing temperature and processing time in the microwave plasma reaction region 36 are as follows. Pressure 10-100 torr. Preferably 20-40 torr. Processing temperature: 90-900°C. Preferably 300-500°C. Treatment time: 0.2-20 hours (hrs). Preferably 0.5 to 5 hours (hrs).

[0024] Furthermore, the microwave output is 2.45 gigahertz (Ghz) and 50 to 500 W, and preferably,
It is 100-300W.

The thickness of the diamond thin film layer formed on the surface of the phosphor particles can be freely adjusted by changing the residence time in the microwave plasma reaction region 36, processing time, gas concentration, or gas composition.

In the case of this diamond coating device, the residence time τ (time) of the phosphor particles in the plasma is given by the following equation. τ=0.0004θL/ΔnD Here, θ is the powder repose angle (degrees), and L is the plasma total length (m
m), Δ is the rotating reaction vessel gradient, n is the rotation speed (rpm) of the rotating reaction vessel, and D is the diameter (mm) of the rotating reaction vessel.

(Example 1) A specific example will be described below.

A rotating reaction vessel 4 made of quartz having an inner diameter of 40 mm was set at a gradient of 1/400, and the rotation speed was 10 rpm. Further, the plasma wave oscillator 32 was used to generate microwaves of 2.45 gigahertz. The powder feeder 12 contains average particles 4
Filled with μm Y2O2S:Eu phosphor particles. By preparing the back pressure gas source 14 and the raw material gas source 10, the composition of the raw material gas in the microwave plasma reaction region 36 is set to 0.5% methane (hydrogen ratio), 20% water vapor (methane ratio),
Hydrogen sulfide 20% (methane ratio), treatment temperature 500℃
, pressure is 20 torr, microwave power is 30
0W, and under these conditions, the residence time determined from the above equation was 0.7 hours.

As a result of depositing diamond on the surface of the phosphor in this manner, a diamond thin film layer of about 0.01 μm was formed. When confirmed using an electron microscope photograph, as shown in FIG. 3, the surface of the phosphor particles 40 was coated with a diamond thin film layer 42 almost uniformly. Further, by conducting Raman analysis on the diamond thin film layer 42, it was confirmed that the diamond thin film layer 42 was made of high quality diamond.

When a phosphor film for a cathode ray tube was prepared using the obtained phosphor particles, that is, the diamond-coated Y2O2S:Eu phosphor particles, it was found that the Y2O2S:Eu of this example
The phosphor particles are uniformly coated with diamond on the surface of each particle through a gas phase reaction, so the adhesion between the phosphor particles and the glass plate to which they are applied is extremely uniform, and the dispersibility of the coating is also excellent. was.

[0031] When the characteristics of the fluorescent film were investigated, it was found that the heat dissipation property was extremely good compared to conventional Y2O2S:Eu phosphor particles that are not coated with diamond, and the temperature of the fluorescent film did not rise due to electron beam irradiation. Since it can be kept extremely low, deterioration of the phosphor due to temperature quenching can be suppressed. As shown in FIG. 4, as the temperature of the fluorescent film increases,
In the conventional phosphor film using Y2O2S:Eu phosphor particles that are not coated with diamond, as shown by the dotted line in FIG.
While the brightness drops to 50% or less at 100°C, in the phosphor film using the Y2O2S:Eu phosphor particles of this example, the brightness only drops by about 5%, as shown by the solid line in FIG.
Much improved. In addition, in terms of life, there was no ion burnout or composition change on the particle surface, and in particular, there was no formation of color centers due to diffusion of impurities from the outside, and the product was excellent.

Next, by changing the slope and rotation speed of the rotating reaction vessel 4 of the diamond coating apparatus, the thickness of the diamond thin film layer 42 is set to various values, and the obtained phosphor particles are used to form a diamond thin film. The relationship between the layer thickness and the relative brightness of the fluorescent film at 50°C was investigated. The results are shown in FIG.

In FIG. 5, the brightness of the phosphor film using phosphor particles not coated with diamond was set to 100%. As is clear from Fig. 5, the thickness of the diamond thin film layer is 0.1 μm from the viewpoint of luminance as well as heat dissipation characteristics of the fluorescent film.
The following is preferable from the viewpoint of luminance. Preferably, it is 0.01 μm.

(Examples 2 and 3) As the phosphors, a ZnS:Ag,Al phosphor with an average particle diameter of 4.2 μm and a Y3Al5O12:Tb phosphor with an average particle diameter of 4.5 μm were each used with a thickness of 0.01 μm. was coated with a diamond thin film layer 42 of .

In both cases, the adhesion between the glass and the phosphor particles can be significantly improved, and the phosphor film has excellent heat dissipation properties.In addition, in terms of life, there is no ion burnout or compositional changes on the particle surface. In particular, there was no formation of color centers due to the diffusion of impurities from the outside, which was excellent.

[0036]

[Effects of the Invention] As explained above, according to the present invention,
By forming a diamond thin film layer on the surface of the phosphor particles using the microwave plasma method, diamond's excellent thermal conductivity, light transmission properties, and chemical stability can be utilized, resulting in improved temperature quenching and chemical stability. Furthermore, according to the production method of the present invention, a diamond thin film layer can be formed on the surface of the phosphor particles by a microwave plasma method in a simple and industrially continuous manner. can be formed.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a diamond coating device according to the present invention, partially in section.

FIG. 2 is an enlarged cross-sectional view of the cross section taken along line A in FIG. 1;

FIG. 3 is a schematic cross-sectional view showing a diamond-coated phosphor according to an example of the present invention.

4 is a graph diagram showing the relationship between film temperature and relative brightness in a phosphor film coated with the phosphor of FIG. 3; FIG.

FIG. 5 is a graph diagram showing the relationship between the thickness and relative brightness of a diamond thin film layer according to an example of the present invention.

[Explanation of symbols]

4 Rotating reaction vessel 10 Raw material gas source 12 Phosphor raw material 14 Back pressure gas source 18 Collector 24 Bag filter 28 Microwave cavity 30
Waveguide 32 Microwave oscillator 36 Microwave plasma reaction region 40
Phosphor 42 Diamond thin film layer

Claims (2)

[Claims] 1. A phosphor comprising a diamond thin film layer deposited by a microwave plasma method on the surface of phosphor particles. 2. Microwave plasma is generated in a part of a rotating reaction vessel that is airtightly isolated from the outside air and maintained at a reduced pressure inside, and hydrogen-
At the same time as introducing the methane mixed gas, phosphor particles are continuously supplied to the microwave plasma generation region by rotating and tilting the rotating reaction vessel, thereby forming a diamond thin film layer on the surface of the phosphor particles. Characteristic manufacturing method of phosphor.